Spray irrigation systems are currently used widely in agriculture to provide the water requirements for growing crops (e.g., corn). It is common practice to inject fertilizer into the water which is fed into the irrigation pipes so as to fertilize the crop simultaneously with watering. This is convenient, economical and can be done without use of labor. The time of application is optional, and the rate of feeding of the fertilizer is predetermined and is set in order to provide uniform application to an entire field of crops.
In the usual practice the fertilizer used is a solution of nitrogen compounds or other water soluble materials. Usually, a manually adjustable feed pump is used to meter and feed the fertilizer solution into the water stream flowing through the supply pipe of an irrigation system.
One of the most commonly used irrigation systems is the pivot type, wherein a length of pipe supported by drive wheels is connected at one end to a vertical feed pipe through a rotary joint. Numerous spray nozzles are appropriately arranged along the length of the horizontal pipe (referred to as a boom) through which the water sprays over the crops as the boom pivots around the center of the field.
The horizontal pipe or boom often is one quarter mile long, and thus a circle one-half mile in diameter is covered by one irrigation system. This amounts to about 130 acres being irrigated out of a 160-acre quarter section of farm land. Much longer irrigators are used as well.
The fertilizer solution is usually contained in a tank, located at the center of the pivot. An adjustable feed pump accurately meters the flow of fertilizer from the tank and injects it into the water as it flows under pressure to the pivot. The boom (horizontal irrigation pipe) is supported by power-driven wheels, which rotate the boom around the central pivot, and often results in one revolution of the boom in about 48 hours. Often about an inch of water is uniformly applied during a single rotation of the boom. The water flow rate and speed of rotation are manually adjustable.
The liquid fertilizer feed rate is commonly adjusted to an appropriate desired rate, and left at this fixed rate, until it is desired to change the rate. This is often done during the growing season of the crop. The rate of application of the fertilizer at different stages of crop growth is selected according to the best judgment or desires of the pivot supervisor or farm manager.
Various automated sprinkler systems have been previously described, including center pivot systems and lateral systems. Some of such systems include the capability of applying agricultural chemicals of one type or another to the crops. For example, some systems include means for applying herbicides, insecticides, pesticides, or fertilizer to the crops, either by dissolving such chemicals in the irrigation water to be applied to the crops or by including a separate sprinkler system carried by the irrigation sprinkler system. See, for example, U.S. Pat. Nos. 2,726,895; 3,326,232; 3,410,490; 3,464,626; 3,648,930; 3,669,353; 3,680,778; 3,703,990; 3,844,481; 3,901,442; 4,067,497; 4,277,026; and 4,397,421.
None of such prior systems, however, describe any means for determining what is the most efficient rate of application of agricultural chemical (e.g., fertilizer or other agricultural chemical) in an irrigation system. Thus, a farmer or grower is left to guess at the proper application rate, or to use trial and error techniques over a period of years, or to attempt to approximate the application rate recommended by agricultural agents or various agricultural publications.
The problem is compounded by the fact that soil will vary in constituency from one area of a county to another, or even from one field to another. Soil will also vary in presence of available nutrients from one location to another. Further, weather conditions will vary from one area to another and there is some belief that certain weather phenomena can have an effect on the amount of certain elements found in the soil.
Moreover, the types of crops grown on a particular field in a prior season will affect the types and amounts of nutrients remaining in the soil. Other factors can also affect this.
As a result, efficient use of fertilizer, for example, is very difficult to achieve. Also, the timing of fertilizer application can be critical to achieving the most effective use of the fertilizer. For example, if the fertilizer is not applied to the growing crops in the proper amount and at the proper time there will not be efficient use of the fertilizer.